The present invention relates to a device for optimizing the distribution of a fluid containing for example, at least one gas phase and at least one liquid phase through a bed of granular solids or particles, the fluid being in downward circulation through this bed.
The present invention is particularly applicable to the field of gas/liquid distributors where the gas phase is composed at least partially of hydrogen, for example for selective or total hydrogenations of C.sub.3 to C.sub.5 cuts, selective hydrogenation of steam-cracked gasolines, hydrogenation of aromatic compounds in aliphatic and/or naphtha cuts, hydrogenation of olefins in aromatic cuts, dearsenification and/or hydrodemetallization of liquid cuts, and hydrodesulfurization, hydrocracking, isomerization, and fixed-bed catalytic reforming reactions.
The invention can also applied to implement other reactions requiring good mixing of a gas phase and a liquid phase, for example partial or total oxidation reactions, aromatic and aliphatic alkylation reactions, and amination, acetyloxidation, ammoxidation, and chlorination reactions.
In this field, one of the key points for achieving good hydrogenation selectivity is proper distribution of the gas and liquid at the head of the reactor or at the head of each catalyst bed in view of the fact that the gas/liquid volumetric ratios generally range from 0.01 to 50 and most frequently from 0.02 to 20.
One possibility used in the prior art consists, for example, as described in the book "Chemical Reactors" by P. Trambouze et al., published by Editions Technip, 1988, on pages 287 and 456, of using distributor plates having a plurality of holes dedicated to passage of the liquid and a plurality of chimneys for passage of the gas. The circulation or passage paths of the liquid and gas phases are different as gas and liquid distribution is in separate phases. The two phases are mixed inside the free space located below the distributor plate. This document recommends using a minimum number of liquid distribution holes to achieve good initial distribution of the phases.
In order to improve distribution of the gas at the head of the catalytic bed and inside the latter, a number of documents describe distributor plates designed to improve distribution of the gas while retaining good distribution of the liquid.
U.S. Pat. No. 4,836,989 refers to various disadvantages resulting from the use of identical passage paths for the liquid phase and the gas phase, which can arise from irregularities in the fluid passage apertures or from the influence of the position of the distributor plate relative to the catalytic bed. To remedy these disadvantages, the technical teaching contained in this document leads an individual skilled in the art to use a specific arrangement of several plates provided with collection and distribution means for the liquid and gas phases separately or in the form of a mixture. A first plate provided with accumulation and passage means for the two phases is associated with means disposed below the plate and allowing these two fluids to spill into a mixing chamber. When they leave this chamber, the two phases are sent separately to the passage orifices of the liquid phase disposed on a second plate and to chimneys each of which has in its upper part an orifice allowing the gas phase to pass. The two phases are thus distributed separately in the space formed by this second plate and a third plate including chimneys provided with passage orifices for the liquid phase and the gas phase and allowing distribution of both phases in the form of a mixture.
Another arrangement that avoids the influence of the level at which the distributor plate is positioned on the distribution of the two phases in the catalytic bed is described for example in U.S. Pat. No. 4,126,540.
The device described in this document has two plates disposed one above the other. The first plate has several orifices allowing the flow of fluid to pass and the second plate has chimneys provided with side orifices and a top orifice. The arrangement of the axes of the orifices for passage of the first plate are offset from the axes of the chimneys such that the liquid is deflected from the top orifices of the chimneys to pass largely through the side orifices. The density of the chimneys on the lower plate is chosen from the values usually recommended by the prior art. This density value is, for example, chosen between 2 and 64 chimneys per square meter, each of these chimneys being provided with a number of passage holes or orifices that is between 1 and 20. The surface area of each of the passage orifices can vary between 0.3 and 19 cm.sup.2. The chimney diameter is such that its central aperture ranges from 18 to 645 cm.sup.2. This document also teaches positioning the distributor plate relative to the catalytic bed at a distance of at least 7.62 cm and at most 91 cm from this bed.
With such an arrangement, it has been shown that a similar liquid flow is obtained in each chimney. Hence, the device described in this patent avoids substantially different liquid flows in the chimneys, even when the horizontality of the plate is imperfect. This document does not show that the device as described affords better homogeneity for the flow characteristics in the catalytic bed.
Thus it is known to the individual skilled in the art that, by using the usual chimney density values mentioned in the prior art, optimum mixture distribution homogeneity can be obtained.
None of these documents, thus, refers to the possibility of reliably using a distributor plate comprising several chimneys in a simple configuration, for example the plate being used alone, to obtain a good distribution of these phases at the head of the catalytic bed and within the latter.